Re: [Bridge] [PATCH net] net: bridge: mcast: Do not allow users to set IGMP counter/timer to zero

[Hangbin Liu <liuhangbin@gmail.com>]

Hi Nikolay,

On Mon, Oct 18, 2021 at 01:28:14PM +0300, Nikolay Aleksandrov wrote:
> On 18/10/2021 11:26, Hangbin Liu wrote:
> > There is no meaning to set an IGMP counter/timer to 0. Or it will cause
> > unexpected behavior. E.g. if set multicast_membership_interval to 0,
> > bridge will remove the mdb immediately after adding.
> > 
> > Fixes: 79b859f573d6 ("bridge: netlink: add support for multicast_last_member_count")
> > Fixes: b89e6babad4b ("bridge: netlink: add support for multicast_startup_query_count")
> > Fixes: 7e4df51eb35d ("bridge: netlink: add support for igmp's intervals")
> > Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
> > ---
> >  net/bridge/br_netlink.c  | 73 +++++++++++++++++++++++++++++---------
> >  net/bridge/br_sysfs_br.c | 75 +++++++++++++++++++++++++++++++---------
> >  2 files changed, 116 insertions(+), 32 deletions(-)
> > 
> 
> Nacked-by: Nikolay Aleksandrov <nikolay@nvidia.com>
> 
> For a few reasons,
> I'll start with the obvious that - yes, users are allowed to change the values to non-RFC
> compliant, but we cannot change that now as we'd risk breaking user-space which is probably
> doing that somewhere with some of the values below. We can fix any issues that might arise
> from doing it though, so it doesn't affect normal operation. If changing some of the options
> to 0 or to unreasonably high values lead to problems let's fix those and we could discuss
> adding constraints there if necessary.

I started this patch when I saw there is not limit for setting
multicast_membership_interval to 0, which will cause bridge remove the
mdb directly after adding. Do you think this is a problem.

And what about others? I don't think there is a meaning to set other intervals
to 0.

> 
> The second issue is that you're mixing different checks below, you say do not allow zero
> but you're also checking for RFC compliance between different values.

Do you mean the RFC3376 8.3 rule? I can fix it in another patch.

> 
> The third issue is that you haven't done the same change for the same values for per-vlan
> multicast options (we have the same options per-vlan as well).

Ah, thanks, I could fix that.
> 
> Your fixes tags are wrong, too. Most of these values could be set well before they were
> available through netlink.

Oh... Then how should I set the fixes tag? Since I want fix both the netlink
configs and sys configs. Add a new one d902eee43f19 ("bridge: Add multicast
count/interval sysfs entries")

> 
> Note on the style - generally I'd add helpers to set them and add the constraints in those
> helpers, so they can be used for both netlink and sysfs. It would definitely target net-next
> unless it's an actual bug fix.

How about a helper like:

int br_multicast_set_interval(unsigned long *mcast_val, u64 val)
{
	if (val) {
		mcast_val = clock_t_to_jiffies(val);
		return 0;
	} else {
		NL_SET_ERR_MSG(extack, "Invalid multicast interval, should not be 0");
		return -EINVAL;
	}
}

Thanks
Hangbin